With increase of the mortality due to infectious diseases and appearance of drug resistance bacteria, speeding-up of antimicrobial susceptibility tests of infectious disease-causing bacteria is attracting attentions.
Conventionally, antimicrobial susceptibility tests have been implemented based on a culture method. An antimicrobial susceptibility test based on a culture method is conducted according to the following procedure. First, a specimen, such as blood, pharynx wiping liquid, and sputum, is collected from a patient of an infectious disease. Isolation culture is then performed for a whole day in order to obtain the infectious disease-causing bacterium as a single colony from the specimen containing indigenous bacteria together. The bacteria forming the single colony are prepared into a prescribed concentration and dispensed into vessels in which a drug or antibody of various kinds and various concentrations are placed, and the antimicrobial susceptibility culture is conducted for a whole day. After culturing the bacteria, a result of the antimicrobial susceptibility test of the infectious disease-causing bacterium is obtained based on the presence or absence of the growth of the bacteria, and according to the result, proper drug dosage is applied to the patient. Accordingly, the proper dosage for the patient of the infectious disease is started at three or more days after the collection of the specimen.
On the other hand, as a method for rapidly performing an antimicrobial susceptibility test, an ATP bioluminescence method using, as a measure of the growth of the bacteria, variation of adenosine triphosphate (ATP) which is present in bacteria as an energy source is mentioned. In the ATP method, ATP present in bacteria as an energy source is detected by utilizing luciferase which is an enzyme derived from firefly. Since luciferase oxidizes luciferin, which is a substrate, in the presence of ATP and Mg2+ in the bacteria and the amount of the thus-generated luminescence is proportional to the ATP amount, the growth of the bacteria can be estimated from the variation in the amount of luminescence.
A process for determining the number of bacteria by the use of the ATP method is disclosed, for example, in PTL 1. PTL 1 discloses a technique in which viable cells are counted by the ATP measurement and the total cells are counted by a DNA method, followed by subtracting the viable cell number from the total cell number to obtain the viable cell number and the dead cell number.